1. Field of the Invention
This invention relates to a control system for internal combustion engines, and more particularly to a control system which controls the supply of fuel injected into an intake pipe in a manner compensating for a fuel amount adhering to the inner surface of the intake pipe.
2. Prior Art
In conventional internal combustion engines of the type that fuel is injected into an intake pipe, there is a problem that some of injected fuel adheres to the inner surface of the intake pipe, so that a required amount of fuel cannot be drawn into the combustion chamber. To solve this problem, there has been proposed a fuel supply control method which estimates a fuel amount which is to adhere to the inner surface of the intake pipe and one which is to be drawn into the combustion chamber by evaporation from the fuel adhering to the intake pipe, and determines a fuel injection amount in dependence on the estimated fuel amounts (Japanese Provisional Patent Publication (Kokai) No. 61-126337).
On the other hand, conventionally, evaporative fuel emission control systems have been widely used in internal combustion engines, which operate to prevent evaporative fuel from being emitted from a fuel tank into the atmosphere, by temporarily storing evaporative fuel from the fuel tank in a canister, and purging same into the intake system of the engine. Purging of evaporative fuel into the intake system causes fluctuations in the air-fuel ratio of a mixture supplied to the combustion chamber. To prevent such fluctuations in the air-fuel ratio or a deviation thereof from a desired value due to purging of evaporative fuel, it has also been proposed to estimate an amount of evaporative fuel to be purged, and determine a fuel injection amount based on the estimated evaporative fuel amount (Japanese Provisioned Patent Publications (Kokai) Nos. 1-148043 and 2-27167).
Further, conventionally internal combustion engines are known, in which operating characteristics of intake valves and exhaust valves, i.e., valve timing (valve opening/closing timing and/or valve lift) are changeable, (e.g. Japanese Provisional Patent Publication (Kokai) No. 2-50285).
Furthermore, a fuel injection system is known, in which air (so-called assist-air) is supplied to the fuel injection valves through ports provided in the vicinity thereof to promote atomization of fuel injected from the fuel injection valves (e.g. Japanese Provisional Patent Publication (Kokoku) No. 55-9555).
The above proposed or known systems or methods are intended to solve their respective problems alone. However, in actuality, unless all the problems are solved at the same time, the air-fuel ratio of a mixture supplied to an internal combustion engine cannot be accurately controlled to a desired value. In any event, at least the problem of adherence of fuel to the inner surface of the intake pipe has to be taken into consideration in solving the problems mentioned above. However, a mere combination of two or more of the above-mentioned systems or methods cannot lead to successful control of the air-fuel ratio.